Isolation and identification of a mu-calpain-protein kinase C alpha complex in skeletal muscle.

A mu-calpain-PKC complex was isolated from rabbit skeletal muscle by ultracentrifugation and by anion-exchange chromatography. The PKC associated to mu-calpain was stimulated by calcium, phosphatidylserine and diacylglycerol, and corresponds to a conventional PKC (cPKC). This complex presents an apparent molecular mass close to 190 kDa and is composed of one mu-calpain molecule and of one cPKC molecule. Using monoclonal antibodies specific for the different cPKC isoforms, the isoenzyme associated to mu-calpain was identified as cPKC alpha. Immunofluorescence staining reveals a co-localization of mu-calpain and cPKC alpha on the muscle fibre plasma membranes.